Simultaneous determination of naproxen, ibuprofen and diclofenac in wastewater using solid-phase extraction with high performance liquid chromatography

The presence of pharmaceutical compounds in the environment is a growing concern to analytical chemists and the general public. Pharmaceutical compounds such as naproxen, ibuprofen and diclofenac are useful compounds that belong to the group of non-steroidal anti-inflammatory drugs (NSAIDs). These organic compounds are polar and acidic. Both naproxen and diclofenac have a pKa value of 4.2, whereas that of ibuprofen is 4.9 (Table 1) (Dahane et al., 2013). NSAIDs are widely used by humans for the treatment of rheumatoid arthritis (Mahkam and Poorgholy, 2011). Once consumed, they are subjected to human metabolism, followed by excretion in urine and faeces as metabolites and as unaltered parent compounds, which can be subjected to further transformations in wastewater treatment plants (WWTPs) (Parrilla Vazquez et al., 2013). Overdose or chronic abuse of NSAIDs can lead to toxic side-effects (Lagha et al., 2011). Health effects caused by the consumption of acidic pharmaceuticals by animals at low levels is not understood; however, diclofenac has been reported to be the cause of vulture population declines in Asia (Oaks et al., 2004; Taggart et al., 2007). Diclofenac is also known as a compound that affects organ histology and gene expression in fish at concentrations as low as 1 μg·L-1 (Cuklev et al., 2012). Therefore, the development of a very sensitive analytical methodology for the study of NSAIDs in various sample matrices is required. In many countries, the removal efficiency for NSAIDs during the wastewater treatment process has been investigated (Lindqvist et al., 2005; Yu et al., 2006; Zorita et al., 2009). For example, in a municipal sewage treatment system located in the south of Sweden, a removal efficiency of 94% and 99% for naproxen and ibuprofen, respectively, was reported (Zorita et al., 2009). However, in the same study, diclofenac was not removed during the wastewater treatment process. The removal efficiency for ibuprofen, naproxen and diclofenac in a WWTP located in Germany was 87%, 88% and 18%, respectively (Yu et al., 2006). In WWTPs located in Finland, the removal efficiencies were in the ranges of 78–100%, 55–98% and 9–60% for ibuprofen, naproxen and diclofenac, respectively (Lindqvist et al., 2005). All these studies show the incomplete removal of such compounds from WWTPs. As a consequence of this, such compounds have also been detected in river water samples from Spain (Carmona et al., 2014). The same authors reported the occurrence of ibuprofen, naproxen, diclofenac and other pharmaceutical compounds at ng·L-1 levels in tap and mineral water samples collected from Spain. The occurrence of pharmaceutical compounds in WWTP effluents, surface water and drinking water samples in Europe demands a detailed screening of such compounds on a worldwide scale. Although there is enough evidence on the occurrence of NSAIDs in European water bodies (Carmona et al., 2014; Yu et al., 2006; Rodil et al., 2012; Togola and Budzinski, 2007), the presence of such compounds in the South African environment is not fully known. Relatively few published reports on the occurrence of NSAIDs in South African WWTPs have emerged To whom all correspondence should be addressed. e-mail: [email protected] Received 6 June 2016; accepted in revised form 20 March 2017 ABSTRACT The occurrence and removal efficiency for naproxen, ibuprofen and diclofenac in two of eThekwini Municipality’s wastewater treatment plants (WWTPs), Kingsburgh and Umbilo, were investigated. This paper describes a simple method that can be used routinely for the simultaneous determination of such compounds in the influent and effluent of the WWTPs. Target compounds were extracted from wastewater and pre-concentrated using the optimized Oasis MAX solidphase extraction (SPE) method. During SPE, the pH of wastewater samples was adjusted to 2.5; then 100 mL of each sample was loaded onto a pre-conditioned cartridge. The SPE cartridge was rinsed with methanol:water (10:90%, v:v) prior to sequential elution of retained analytes with 2 mL methanol, followed by 2 mL methanol and acetic acid (90:10, v:v) and 2 mL of 2% (v:v) formic acid diluted using a mixture of methanol and acetic acid (40:60, v:v). The eluted analytes from the SPE cartridge were quantified using high performance liquid chromatography (HPLC) equipped with photo diode array detection. The analytical method was validated by spiking deionized water with 5 and 50 μg·L-1 of target compounds, for which the recovery range of 76 to 98% was achieved with good precision. The instrument quantification limits obtained were 0.1 μg·L-1, for naproxen and 0.4 μg·L-1 for both ibuprofen and diclofenac. The detected concentrations for naproxen, ibuprofen and diclofenac in the influent of both WWTPs were in the ranges of 15–20 μg·L-1, 55–69 μg·L-1 and 6.4–16 μg·L-1, respectively. In effluent, the detected concentrations for naproxen, ibuprofen and diclofenac were in the ranges of 0.6–1.1, 2.1–4.2 and 1.4–2.0 μg·L-1, respectively. Overall, the employed SPE-HPLC method led to rapid pre-concentration of target compounds prior to their trace quantification in wastewater samples.